The wireless telecommunication industry continues to experience significant growth and consolidation. In the United States, market penetration is near 32% with approximately 86 million users nationwide. In 1999 the total number of subscribers increased 25% over the previous year, with the average Minutes of Use (MOU) also increasing by about 20% per user. If one considers growth in the digital market, in as short as three years, the digital subscriber base has grown to 49 million users, or approximately equal to the installed number of users of analog legacy systems. Even more interesting is an observation by Verizon Mobile that 70% of their busy hour traffic (an important system design parameter) is digital traffic, although only approximately 40% of the total number of their subscribers are digital users. The Verizon Mobile observation indicates the digital subscriber will drive the network design through its increasing usage, whereas the analog user is truly a passive xe2x80x9cgloveboxxe2x80x9d subscriber. Similar growth has been witnessed in other countries, especially in Northern and Western Europe, where market penetration is even higher, approaching 80% in some areas, and digital service is almost exclusively used.
With the availability of Personal Communications Service (PCS) frequencies in the United States, and additional continuing auctions of spectrum outside of the traditional 800-900 MegaHertz (MHz) radio band, the past few years have also seen increased competition among service providers. For example, it has also been estimated that 88% of the U.S. population has three or more different wireless service providers from which to choose, 69% have five or more, and about 4% have as many as seven service providers in their local area.
In 1999 total wireless industry revenue increased to $43B, representing an approximate 21% gain over 1998. However, a larger revenue increase would have been expected given the increased subscriber count and usage statistics. It is clear that industry consolidation, the rush to build out a nationwide footprint by multiple competing service providers, and subsequent need to offer competitive pricing plans has had the effect of actually diminishing the dollar-per-minute price that customers are willing to pay for service.
These market realities have placed continuing pressure on system designers to provide system infrastructure at minimum cost. Radio tower construction companies continue to employ several business strategies to serve their target market. Their historical business strategy, is build-to-suit (i.e., at the specific request and location as specified by a wireless operator). But some have now taken speculation approach, where they build a tower where it may be allowed by local zoning and the work with the new service providers to use the already existing towers. The speculative build spawned by the recently adopted zoning by-law is actually encouraged by communities to mitigate the xe2x80x9cunsightly uglinessxe2x80x9d of cellular phone towers. Towns adopted the by-laws to control tower placement since Federal laws prohibit local zoning authorities to completely ban the deployment of wireless infrastructure in a community. Often the shared tower facility is zoned far removed from residential areas, in more commercialized areas of town, along heavily traveled roads, or in more sparsely populated rural sections. But providing such out of the way locations for towers often does not fully address each and every wireless operator""s capacity or coverage need.
Each of the individual wireless operators compete for the household wireline replacement, and as their dollar-per-MOU is driven down due to competition in the xe2x80x9ctraditionalxe2x80x9d wireless space, the xe2x80x9cat homexe2x80x9d use is one of the last untapped markets. As the industry continues to consolidate, the wireless operator will look for new ways to offer enhanced services (coverage or products) to maintain and capture new revenue.
Considering the trends that have appeared over recent years, when given the opportunity to displace the household wireline phone with reliable wireless service, a wireless service operator may see their average MOUs increase by a factor of 2 to 4, thereby directly increasing their revenue potential 200 to 400%. In order to achieve this, the wireless operator desires to gain access throughout a community as easily as possible, in both areas where wireless facilities are an allowed use and in where they are not, and blanket the community with strong signal presence.
One aspect of the present invention is directed towards retransmission techniques. In an illustrative embodiment, a received signal includes data information that is transmitted to a following node in a communication system for eventual transmission of the data information over a wireless communication link. The data information is processed by hardware that produces overhead bits supporting a serial transmission of the data information over a communication medium to a following node. For example, the data information of the received signal and overhead bits can be combined or framed according to a serial transport protocol for transmission over the communication medium. This technique of mapping or framing the data information into a serial transport protocol is used to more efficiently transmit the data over the communication medium to a target receiver.
In a retransmission system, the received signal passes from receiving hardware, over a communication link, to transmission hardware. The received signal can consist of data from an analog to digital converter (ADC). The receiving hardware also has status information about the signal, the hardware that needs to pass over the link from receiver to transmitter.
One aspect of the retransmission system involves passing the digitized signal unmodified from receiver to transmitter. The retransmission system can provide fault detection, system status, and control features to control software that manages the link. For example, the transmitter can be notified when a retransmission link contains bad data, thus, preventing transmission of corrupted signals.
Three options can be considered in the design of control, status and fault detection. A first option passing only data over the retransmission link and using a separate software to software communication channel for status. A second option is to multiplex control and status data into a serial data stream, an xe2x80x9cinbandxe2x80x9d approach. This approach can include state machines in the data channel to find and distinguish the overhead from the data and reduces the available data rate. A third option is to pass the control and status data over a xe2x80x9csideband.xe2x80x9d
The SONET protocol can be used in a retransmission system since a number of commercial circuit cards include multiplexing capability at a sufficient data rate. This protocol used can include the sideband option. Specifically, SONET uses Path overhead to carry control and status information from one end of the link to another.
In one application, the signal is received in a digitized RF (Radio Frequency) format that reformatted and transmitted to a following node using a serial protocol such as SONET (Synchronous Optical Network). The original signal can be reconstructed at a downstream or receiver node using the data information. The overhead bits can be used to conform that the data is valid and provides information to manage retransmission in the network. Accordingly, one aspect of the present invention involves transmitting a digitized RF signal over SONET.
The received signal can be derived from an RF signal transmitted over a coaxial cable. More specifically, a band of frequencies of the RF signal on the coaxial cable can be down converted to produce an analog IF (Intermediate Frequency) signal that is thereafter converted using an analog-to-digital (A/D) converter. The A/D converter digitizes the IF bandwidth signal into digital words that are the data information transmitted over the serial stream. The overhead bits are added and the combined signal is sent over a high speed transport network, such as one that uses an optical fiber as the physical transmission medium. The data information and overhead bits can be received in a parallel format and converted to a serial format for transmission over the communication medium. For instance, the signal can be an analog signal that is sampled to produce 14-bit words that are converted to digital words for transmission over a serial transport protocol. At a downstream receiver node, the serial stream (that is potentially transmitted and received over an optical fiber) can be converted back into a digitized RF signal using the data information. The overhead information provides fault detection and configuration information to the transmitter hardware and its managing software. The reconstructed RF signal can then be used to drive an antenna for transmitting the data information to a target such as a cellular phone device.
Thus, one aspect of the present invention is directed towards a seamless solution for converting an RE signal for transmission over an optical link and conversion back to the RF signal for driving a remote antenna device. The use of an optical fiber provides high bandwidth for transmitting large amounts of data.
As mentioned, the serial stream can be transmitted through multiple nodes to a target receiver. In general, a node can be any point in the communication system such as a circuit component, a circuit card, or a device that processes, stores, receives or transmits data information. To aid in re-transmission from one node to another, a particular protocol can be selected for transmitting the serial stream. Based on an anticipated protocol for transmitting the serial stream at a following downstream node, at least a portion of the overhead bits generated at an upstream node can be transmitted in an allocated register of the selected transport protocol that later will be used at the downstream node. In other words, certain bits or registers of the transport protocol previously used for transmitting the serial stream from the upstream node to a downstream node can be overwritten and used for a different purpose when the serial stream is re-transmitted from a following downstream node. Consequently, registers and bits of the selected protocol can be used for different purposes from one node to the next. Upon receipt of the re-transmitted serial stream according to the selected protocol, the serial stream can be checked for configuration and transmission errors and processed to reproduce the signal as it was originally received.
In a specific application, the serial stream is initially transmitted using a Quasi-SONET protocol from one node to the next and certain registers of the Quasi-SONET protocol are used for overhead such as diagnostics and control information. This enables two nodes such as an intermediate transmitter/receiver pair to pass information between each other for maintaining a link or, on a larger scale, an overall communication system. At a node receiving the serial stream of data information, the serial stream can be further re-transmitted using the SONET protocol.
The communication medium can be a fiber optic link carrying data originally intended for transmission over an RF (Radio Frequency) antenna device to a mobile cellular phone user. Thus, a digitized RF signal can be processed for transmission to a target antenna device via the SONET protocol. The communication medium can also be a hard-wired cable such as a coaxial cable or twisted pair of wires for carrying a differential signal. It should be understood that types of communication media can be connected in tandem to support propagation of the serial stream including data information and overhead bits. More specifically, the serial stream can be transmitted over a pair of differential copper wires and later converted to an optical signal transmitted over fibers, etc.
The overhead bits for transmitting the data information over the serial stream can include time stamps. In one application, the time stamps are used for location services. For example, a service provider can use the time stamp information to identify the location of a target cellular devices such as a mobile phone user. Additionally, the time stamps can be used to determine a path delay of a serial stream from one node to the next.
The overhead bits can also include parity information to identify quality of the serial stream. For example, the originally received RF signal including the data information can be processed for transmission into a serial stream using parity information such as a checksum to ensure signal integrity. Consequently, data information received in the serial stream can be checked for errors. Health of hardware or a link can also be determined using similar types of maintenance information transmitted in the overhead bits. Parity can be applied to the entire set of bits in a frame such as data bits, overhead bits and frame sync bits.
The system for communicating data information can include a hub to receive a signal from at least one base station. For example, the hub can be designed to receive signals from a base station farm including multiple base stations. As discussed, a received signal can include data information that is to be transmitted to a target by a remote antenna device. The system can include a communication medium to couple the hub and antenna device. A processor device disposed in the hub can decode the received signal to produce overhead bits supporting a serial transmission of the data information over the communication medium to the remote antenna device. Consequently, an RF signal originally intended for driving an antenna device can be repackaged (including overhead bits and the data information) based on a serial transport protocol to a remote receiver over a fiber link.
Based upon receipt of the serial stream, the original RF signal can be reconstructed at the remote receiver to drive a remotely located antenna device. This provides a seamless solution for transmitting an RF signal at the remote antenna device without needlessly degrading system performance. That is, although there is overhead processing associated with reformatting the signal for transmission to a target, the technique of transmitting the data information into the serial protocol including overhead bits enables use of a more robust media for transmitting the data information of the original signal.
One aspect of the transport protocol is to add overhead as a sideband to the data stream to avoid the complexity of time multiplexing the overhead inband with the data stream. It works out that the commercial devices typically have 16 bits available. In one application, 14 bits can be used for data, while one is used for overhead and one is used for frame sync. If 15 bit data words are used, we can move the frame sync function into the overhead bit stream. Within the commercial 16:1 serdes, the bits become time multiplexed.
The hub can include a patch panel for selecting which of multiple target antenna devices a serial stream will be directed. For example, signals from multiple base stations can be fed into the hub where they are redirected or broadcasted to one or multiple target devices. Each signal can be processed for serial transmission over a communication medium such as a fiber link to a remote receiver device including an antenna for transmitting the data information. One purpose of the patch panel is to enable an operator to manually connect input and output ports via a cable so that a serial stream is directed to a particular remote receiver and corresponding antenna device. Thus, a hub and its corresponding hardware and software functions can direct an RF signal to one of multiple remote antenna devices.
The overhead bits can be allocated for specific purposes. For example, a portion of overhead bits supported by the transport protocol can be allocated to indicate a status of a communication link. Additionally, a portion of the overhead bits can be used to control functions at a downstream node that is used to generate an RF (Radio Frequency) signal. For instance, control information can identify a frequency at which an Rf signal is to be transmitted.
In one application, the overhead bits include path trace information to identify a source of a received serial stream including data information. Additionally, the path trace information can be used to configure at least a portion of the communication system.
Most fiber-based repeater products modulate an RF signal directly onto an optical transport. While this method of transmitting RF may be viable for in-building applications, there are several factors that can be concern over a long haul. These factors include the different air interface RF links which all have very wide dynamic range performance requirements, fiber path loss varying with temperature, signal loss varying with fiber path lengths and splits, and the ease of multiplexing multiple users on a common fiber path. Use of the distributed system according to the principles of the present invention addresses these concerns, providing a highly robust and efficient backbone for transmitting a digitized signal over a serial communication medium. Accordingly, an analog RF signal can be stripped of its carrier frequency, digitized, converted into a serial format, and transmitted to a remote target device where the original RF signal is then reconstructed for driving an antenna.
Many traditional base station towers have been built to handle the antenna and base station assets of one wireless service provider. Use of a distributed RF system supporting the conversion of data and overhead bits to a serial stream protocols allows the use of multi-band antennas at remote locations. Thus, a single tenant tower can be inexpensively turned into a multi-tenant cell site, alleviating ground space constraints at tower sites. Also, the distributed RF system enables multiple base stations to share a common RF distribution backbone to transmit and receive data from remote antenna devices mounted on existing infrastructure such as low height telephone poles. Thus, a zone of RF coverage can be enlarged without signal degradation by leveraging existing infrastructure, such as fiber-optic lines and microwave spectrum, to transmit wireless signals between mobile users and network base stations.